Counterweight system for tractors having side-mounted attachments



Feb. 22, 1966 H. M. KENNEDY 3,236,391

COUNTERWEIGHT SYSTEM FOR TRACTORS HAVING SIDE-MOUNTED ATTACHMENTS Filed Feb. 24, 1964 5 Sheets-Sheet 1 INVENTOR. I Ze -H HARRY M. KENNEDY If I 1 BY 2; MAHONEY, MILLER & RAMBO Ll ATTORNEYS.

Feb. 22, 1966 KENNEDY 3,236,391

COUNTERWEIGHT SYSTEM FOR TRACTORS HAVING SIDE-MOUNTED ATTACHMENTS Filed Feb. 24, 1964 5 Sheets-Sheet 2 20 30 4? 1 A O A if 2/ I] 52 If] I/ 32 215 i Z/ g a l\ k Z5 /5 /6 27 42 I Z4 Z? E; E E

e "I"! 1 e /8 m A "*1 1h E INVENTOR. HARRY Mv KENNEDY BY MA HONEY. M/LLER61 RAMBO 3.1. E 3 V ATTORNEYS.

Feb. 22, 1966 H. M. KENNEDY 3,236,391

COUNTERWEIGHT SYSTEM FOR TRACTORS HAVING SIDE-MOUNTED ATTACHMENTS Filed Feb. 24, 1964 5 Sheets-Sheet 5 I j I l a l t 1 x i 1 m J E m r INVENTOR. HARRY M KENNEDY BY MAHONEY, M/LLER 2 RAMBO A TTORNEYS.

Feb. 22, 1966 H. M. KENNEDY 3,236,391

COUNTERWEIGHT SYSTEM FOR TRACTORS HAVING SIDE-MOUNTED ATTACHMENTS Filed Feb. 24, 1964 5 Sheets-Sheet 4 INVENTOR. HARRY M. KENNEDY BY MAHONEY. M/LLER 8 RAMBO ATTORNEYS.

United States Patent 3,236,391 COUNTERWEIGHT SYSTEM FOR TRACTORS HAVING SIDE-MOUNTED ATTACHMENTS Harry M. Kennedy, Bucyrus, Ohio, assignor to The Superior Equipment Company, Bucyrus, Ohio, a corporation of Ohio Filed Feb. 24, 1964, Ser. No. 346,963 1 Claim. (Cl. 212-8) This invention relates to a counterweight system for tractors having side-mounted attachments. The counterweight system of this invention will be described specifically with relation to a tractor of the crawler type having a side-mounted boom attachment but it is to be understood that it is applicable to tractors having other side-mounted attachments which need to be counterbalanced during operation.

According to this invention, the counterweight system is applied to the basic carrying tractor without any substantial alteration of the tractor. The system is applied to the tractor in a most efiicient manner to obtain maximum counterweight eificiency so that maximum lift efiiciency can be obtained with the side boom. The application to the tractor is also such that maximum retraction of the counterweights within the overall extent of a standard tractor is accomplished even though maximum extension can be obtained when desired to efiectively counterbalance the lift at the side boom. These results are further obtained with low weight profile and high clearance and by utilizing a simple construction. Furthermore, movement of the weights between their various positions and synchronization of the movements is accomplished in a novel and efiicient manner.

More specifically, the counterweights of this system are mounted at the side of the tractor opposite to the side where the side-boom is mounted. Counterweight racks are hinged in a vertical horizontal plane within the respective side confines of the basic tractor and can be rotated 90 in a horizontal plane about respective vertical pivots or hinge axes spaced longitudinally in that plane. The racks are preferably provided in a pair so that in retracted position of the racks the counterweights are in opposed longitudinally spaced relationship where they are completely within the side and ends of the tractor and are disposed directly over the crawler track thereof in parallel relationship to the longitudinal center line of the the weights carried thereby are revolved about the pivot tractor. When the side boom is to be operated, the racks and the weights carried thereby are revolved about the pivot axes simultaneously to the same extent to fully extended position, each in that extended position being in a plane at a right angle to the pivot axes plane and the said center line of the tractor. In this latter position, the counterweights give maximum counterbalancing effect to any loading applied to the opposed boom side of the tractor.

The counterweights used on the racks are preferably uniform blocks of heavy material which can be placed in selected numbers on the racks and locked securely thereon. The racks are so designed and so mounted, as indicated above, as to give the most efiicient counterbalancing effect when extended and maximum tractor mobility when retracted. The motivating force for extending and retracting the counterweight racks and the weights carried thereby in the manner indicated above is a novel system of hydraulic rams and associated hydraulic controls.

In the accompanying drawings, a counterweight system embodying this invention is shown, for example, applied to a crawler-type tractor which has a side-boom attachment.

3,236,391 Patented Feb. 22, 1966 ice In these drawings:

FIGURE 1 is a front perspective View of the tractor showing the counterweights in extended positions at one side for balancing the side-boom attachment at the other side.

FIGURE 2 is a top and side fragmentary perspective view showing the side of the tractor which carries the counterweights, the weights being shown in retracted positions.

FIGURE 3 is a view similar to FIGURE 2 but showing the weights in extended or balancing positions.

FIGURE 4 is a fragmentary plan view showing the weight side of the tractor, the weights being shown in full line retracted positions, and indicating by broken lines the extension of one of the weights.

FIGURE 5 is a side elevational view taken along the position indicated at line 55 of FIGURE 4.

FIGURE 6 is an enlarged axial sectional view through one of the weight-positioning rams.

FIGURE 7 is a schematic diagram of the hydraulic system used for moving the weights between their retracted and extended positions.

With reference to the drawings, and especially to FIG- URE 1, this invention is shown applied to a tractor which is illustrated as being of the crawler type. The tractor shown comprises a main frame or chassis 10 which is carried by the crawlers 11 at its opposite sides. The basic tractor chassis carried by the crawlers and the crawlers are of the usual construction. In the example shown at one side of the tractor attached to one of the crawlers is a side boom attachment 12. This attachment is useful for various jobs such as laying pipe in a ditch alongside which the tractor moves. This attachment, for example, may be of the type disclosed in Patent No. 3,092,370 which issued June 4, 1963. It in cludes a cable reeving boom control system 13 which extends from the outer and upper end of the boom of the attachment to the opposite side of the tractor to a yoke 14 which is mounted at that side of the tractor above the associated crawler 11. The specific structure of the side boom attachment is not important to this invention and, therefore, will not be described in further detail. In fact, other attachments which need to be counterbalanced may be used at that side and be counterbalanced by the weight system of this invention disposed at the opposite side.

The counterweight system of this invention is disposed at the side opposite the attachment and is shown as comprising a pair of counterweight-receiving racks 15. These racks are mounted for swinging movement in a horizontal plane about the respective vertical pivots or hinge pins 16. The pair of pivots 16 is disposed in a single vertical plane extending longitudinally of the tractor at one side thereof and located over the associated crawler 11 at the outer edge thereof (FIGURES 1 and 2) so as to obtain maximum counterbalancing effect. This plane is parallel to the center line of the tractor chassis and, as indicated, is outboard as far as possible without having the pivots located beyond the outer edges of the crawler or the width of the tractor. The pivots 16 are disposed in longitudinally spaced relationship.

Each rack 15 is formed to include an outer socket end 17 and an inner mounting end 18. The socket end has a bottom but opens upwardly and outwardly to readily receive counterweights 20 of rectangular or square crosssection complemental to the horizontal cross-section of the socket. The weights are preferably designed so that they may be disposed in stacked position in any suitable number in the respective sockets. Each rack mounting end 18 comprises upper and lower fiat triangular plates 21 and a vertical upright connecting plate 22 which is at the side that will be outermost when the weight racks are retracted and is substantially flush with the correspending side of the socket end. The plates 21 and 22 are all rigidly welded together and will provide inwardly opening sockets, when the racks are retracted, for receiving portions of actuating rams as will later appear.

The pivot or hinge pins 16 are non-rotatably supported by the tractor frame in upright position as indicated in FIGURES 2 to 5. They are rigidly secured at their lower ends to a horizontal shelf or plate 23 of the tractor frame which is directly above the crawler 11 at that side of the tractor, being located at the outer edge of that shelf and spaced longitudinally thereon. The shelf 23 is suitably rigidly braced by brackets 24 from the crawler itself. The upper ends of the pins 16 are braced longitudinally by multiple longitudinal brace bars 25 which are connected thereto. Lateral bracing of the pins is provided by the rigid brackets or standard 26 (FIGURE 4) which extend laterally of the shelf 23 are rigidly secured thereto in upstanding relationship. Connected rigidly between the standards 26 is the longitudinally extending bracing beam 27, located adjacent the upper ends of the pins 16, but spaced below the bars 25, the brace being rigidly secured to the pins. Between the bars 25 and the brace 27, the pins 16 receive bearing sleeves 28 on the inner end portions 18 of the racks 15 which are free to rotate on the pins. Additional sleeves 29 are provided at the lower side of the inner end 18 of each rack 15 which are rotatably mounted on the pins. Thus, each rack 15 is pivoted to its respective pin 16 at upper and lower positions for swinging movement about the axis thereof in a horizontal plane.

The racks 15 are swingable about the pivots 16 from a retracted position, shown in FIGURES 1, 2, and 4, to an extended position as shown in FIGURES 1 and 3. In retracted position, the racks 15 and the counterweights which they carry are completely within the overall extent of the tractor both at the corresponding side and its front and rear ends. In extended position, the racks 15 position the counterweights outwardly from the side of the tractor to a maximum extent.

The movement of the racks 15 is controlled by a pair of hydraulic rams 30. The cylinder 31 of each ram is pivotally carried by the tractor frame for swinging in a horizontal plane about a vertical pivot 32. The pivot 32 is carried by a bracket which is a rigid extension of the standard 26.

The piston rod 34 of the ram at its outer end is pivotally connected at 35 to the associated rack 15 at the inner corner thereof, as indicated best in FIGURE 4. When the racks are retracted, the rams 30 are opposed and in axial alignment. At this time, the racks 15 are in opposed alignment longitudinally over the crawler 11. When the rams 30 are actuated, they are actuated to move the two racks 15 to the same extent. The racks swing outwardly about the pivots 16, forwardly and rearwardly toward each other, until they are in parallel relationship, as indicated best in FIGURE 3, at right angles to the longitudinal center line of the tractor.

Each of the actuator rams 30 is preferably of the construction shown in FIGURE 6 in order to obtain efficient, simultaneous, and uniform movement of both counterweight racks 15 when the two rams are actuated. Each ram 30 is a double-acting single end rod type cylinder and piston unit. The cylinder 31 of each actuator ram is closed at one end by a head end cap 37 having a passageway formed therein communicating with the interior of the cylinder for the hydraulic fluid and connectable exteriorly with the hydraulic system by the conduit 37a which will include a flexible section. The opposite end of the cylinder 31 is closed by a stufiing box 38 which is threaded into the cylinder and forms a fluid-tight seal therewith. Positioned within the cylinder 31 for relative 'reci'procable movement is a piston 33. The piston rod 34 is connected to the piston 39 and extends through the stufling box 38 for connection to the counterweight racks as indicated above. The cylinder 31 is pivotally mounted, as previously described, on the structural framework carried by the tractor. A packing gland 41 is bolted to the stuifing box 38 to form a fluid-tight seal therebetween by means of the packing material 42 disposed in the recess of the stuffing box surrounding the piston rod 34. A rod wiper seal 43 is also carried by the packing gland 41 for exclusion of foreign material from the cylinder. Carried by the piston 31 is the usual seal and ring assembly 44 which forms a fluid-tight seal between the piston and cylinder wall. Also formed in the stufling box 38 is a fluid passageway communicating with the interior of the cylinder and connectable exteriorly thereof to the hydraulic system by a line 38a which will include a flexible portion.

In accordance with this invention, a novel construction is employed in the fabrication of the actuators to provide an automatic retardation or cushioning of the piston movement when either extending or retracting the counterweights. This construction prevents the imposing of extreme shock loads on the apparatus resulting from suddenly stopping of the counterweight racks 15 in either of the extreme positions. The kinetic energy attained by the counterweights during their movement is dissipated through an orifice of suitable dimensions at the terminal end of each stroke. The orifice, according to this invention, is incorporated with the respective passageway and is variable in effect depending on the position of the piston 33 relative to the ends of the cylinder 31.

The passageway 45 in the head end cap 37 includes a cylindrical socket 46 which is coaxial with the cylinder 31. Projecting axially from the piston 39 toward the head end cap 37 is a plunger 48 of cylindrical form and adapted to interfit with the socket 46. The diameters of the socket 46 and the plunger 48 are relatively proportioned to permit the plunger to readily slide into the socket when the piston 39 approaches the end cap 37 at the terminal end of the stroke. With the piston 39 displaced from the end cap 37, as shown in full lines, but moving toward the end cap 37, as in a counterweight retracting cycle, the hydraulic fluid within the cylinder 31 will be displaced through the passageway 45 which is readily entered through the socket 46 which is a relatively large orifice. As the piston 39 approaches the end cap 37, the plunger 48 will begin to enter the socket 46 and block, at least partially, the flow of fluid by restricting the size of the orifice. The position of the piston for this is illustrated in broken lines at A in FIG. 6. Preferably, the end portions of both the socket 46 and plunger 48 are chamfered as shown to reduce the turbulence and prevent a sharp cutoff or reduction in fluid flow at the instant the plunger begins to enter the socket. Reduction of the cross-sectional area of the orifice in this manner increases the force opposing the movement of the piston 39 and is eifective to retard the movement of the piston and associated counterweight which it controls. A further reduction in cross-sectional area of the orifice occurs as the plunger 48 more fully enters the socket 46 where the cylindrical walls of the plunger will be opposed to the adjacent cylindrical wall of the socket. This results in further retardation of the piston 39 until the end face of the piston will have contacted the opposed end face of the cap 37 as illustrated by the broken line position at B in FIGURE 6.

This automatic reduction of the cross-sectional area through which the fluid may exit the cylinder is particularly effective in retarding the movement of the piston 39 and counterweight rack it controls and thereby prevents imposing high shock stresses on the apparatus as the piston reaches the terminal end of the stroke in the retraction stroke of the ram.

Since the actuator 30 is double-acting, the opposite end is similarly constructed. The socket 50 or orifice in this instance is an annular recess formed in the stufling box 38 adjacent the piston rod 34. This recess is approximately of the same cross-sectional area as the socket 46 to permit a similar fluid outflow. An annular collector ring 51 formed in the cylindrical wall of the stuffing box is connected to the socket 50 by a passageway 52, The conduit 38a of the hydraulic system is connected to the cylinder 31 for communication with the socket 50 through the ring 51 and the passageway 52. The collector ring 51 facilitates assembly of the actuator as the stuffing box 38 is threaded into the end of the cylinder 31 and this eliminates the ditiiculties of accurate alignment. The plunger 53 in this instance is an enlarged diameter section of the piston rod 34 adjacent the piston 39. This plunger 53 is adapted to enter the recess or socket S0 and function as previously described to reduce the cross-sectional area of the socket or orifice through which the fluid may flow. Thus, retardation also occurs at the end of the extension stroke of the ram.

The hydraulic circuit for controlling operation of the two actuator rams 30 is illustrated in FIGURE 7 and may be described as follows:

The control valve 60 is a four-way, three-position, spool-type having a hydraulic detent and is manually operated. Incorporated in the construction of the control valve is a relief valve 61 that is connected to the pressure port P for protection of the system. A fixed displacement fluid pump PF is connected to the pressure port P by a conduit 62. Interposed in the conduit 62 is a filter unit 63 for the system fluid which is preferably of the type including a spring-loaded check valve bypass for protection of the filter element as to excessive pressure. A tank or reservoir 64 is connected to the inlet port of the pump. The relief valve 61 is also connected to the reservoir 64 for return of the fluid to the system. The hydraulic detent feature of the control valve is of well known construction and functions to maintain the spool of the valve 60 in either of the two operating positions and, in this application, automatically returns the spool to the center or neutral position when the pistons 39 in the counterweight actuator rams 30 reach the extreme position (either retracted or extended), When the pistons 39 reach the extreme position, fluid flow ceases and the pump will build up pressure in the conduit 62. A pressure relief valve built into the hydraulic detent is set to operate at a predetermined pressure and hydraulically effect a release of the detent. After release of the detent, a spring will return the valve spool to the center position; The predetermined operating pressure of the hydraulic detent would be less than that of the system relief valve 61.

When the spool of the valve 60 is in the center position, the pressure port P is connected to the reservoir 64 by a conduit 65, thereby eliminating any load on the pump and preventing power loss when the valve is centered. At this time, the tank port T and the discharge ports A and B of the valve 60 are blocked. Movement of the valve spool to either of the operating positions interrupts the pressure port P connection to the reservoir 64 and simultaneously connects the pressure port P to the respective discharge port, A or B. The tank port T would be connected to the opposite port, B or A, as the case may be.

The discharge ports A and B are connected by the respective conduits 66 and 67 to the extending and retracting sections of a counterbalance valve 68. Each section of the counterbalance valve comprises the same elements which operate to provide cushioning for stopping the movement of the counterweight racks when the pistons 39 of the actuators are at a midstroke position and to restrict or retard movement of the counterweight racks in relation to the capacity of the pump PF. The etiect of gravity and momentum are minimized by the latter function.

Each section of the valve 68 includes a remotely operated valve 69 which normally prevents fluid flow through the conduit 66 or 67 it controls and a check valve.

type bypasses 70 connected around this valve. The check 6 valve is connected to permit free flow from the respective discharge port, A or B, of the control valve 60 through the check valve. The pilot conduit 71 of each remote valve 69 is connected to the conduit, 66 or 67, of the opposite section of the counterbalance valve 68 at the side of the remote valve connected to the control valve 60. The remote valves 69 are spring biased and are set to open when the fluid pressure in the pilot conduit 71 reaches a predetermined value. The connections of the remote valves 69 and the check valves 70 provide the necessary control over the movement of the counterweight racks 15 and counterweights carried thereby irrespective of the disposition of the tractor relative to a hill. The operation will be further explained hereinafter.

Inter connecting the two sections of the counterbalance valve 68 are a pair of relief valves 72 that operate to cushion the stopping of the counterweights at an intermediate position. At an intermediate position, the pistons 39 of the actuator rams 30 would be partially extended and the cushioning feature built into the actuators would not be effective, assuming that the dashpot plunger portions 48 or 53 of the pistons 39 are not inserted in their respective sockets of the cylinders at this time. Each relief valve 72 is connected between the conduits 66 and 67 subsequent to the remote valves 69 and check valves 79 to permit fluid flow from one conduit to the other when the pressure in the associated conduit reaches a predetermined maximum value. A more detailed explanation of their operation is included hereinafter.

Connected to the conduits 66 and 67 subsequent to the counterbalance valve 68 are the two ram actuators 30. The conduits 37a :of the two rams 30 are connected to the line 66 and the conduits 38a of the two rams are connected to the line 67. The head ends of the rams are connected to one section of the counterbalance valve 68, which section will be termed extend section, by the conduit 66 and the rod ends are connected by the conduit 67 to the opposite section of the valve which is termed retract section. Connected between the extend section of the counterbalance valve 68 and the rams 30 is a flow-divider means which synchronizes the movement of the pistons 39 of the rains and their respectively controlled count-erweights. The flow divider means comprises a pair of gear type, fixed displacement, fluid motors 74 that have the shafts thereof mechanically interconnected as indicated. Similar ports of the motors, either inlet or discharge, are mutually connected to the conduit 66 While the opposite port of each motor is connected to one of the rams. The mechanical interconnection of the fluid motors 74 will thus be seen to synchronize the fluid flow to or from the rams.

Connected to the conduit 66 between the counterbalance valve 68 and the flow divider motors 74 is a relief valve 75 which also has a return conduit connecting with the reservoir. This relief valve is elfective during the cushioning operation of the valves 72 on retraction of the pistons 39 to accommodate the increased flow from the head ends of the cylinders which results from the volume of the cylinders that may be occupied by the piston rods.

Operation of the system is initiated by actuation of the control valve 66 which results in movement of the counterweight racks 15 and the weights carried thereby. With the counterweights in the retracted position, the control valve 60 would be actuated to connect the port A with the port P thereby pressurizing the conduit 66. Simultaneously, the port B would be connected to the port T, venting the conduit 67 to the reservoir 64. After actuation of the control valve 60, the spool would be maintained in the selected position until the fluid pressure in the conduit 62 becomes sufiicient to hydraulically release the detent or the valve when it is manually returned to neutral position. Pressurization of the conduit 66 will cause fluid flow through the check valve 70 and the flow divider motors 74 into the head ends f the actuator ram cylinders 31. The pressurization of he head ends of the actuator cylinders will tend to disllace the fluid from the rod ends but the fluid flow vould be prevented by the remote valve 69 and the heck valve 70 in the retract section of the counteralance valve 68. Increase of the fluid pressure in the onduit 66 as a result of the continued operation of the tump PF to a predetermined value will operate the remote valve '69 through the conduit 71 and open the :onduit 67 to the reservoir 64. The remote valve 69 vill remain open, permitting fluid to flow from the rod =nds of the actuator ram cylinders 31 at all times the luid pressure in the conduit 66 remains above the speciied value and the pistons 39 will continue to extend and lisplace the counterweight racks from their retracted DOSitlOI].

At any time it should be desired to stop the movement of the counterweight racks intermediate their fully etracted and fully extended positions, the spool of the ontrol valve 60 is merely returned to its center position vy manual operation. This blocks the conduits 66 and 7 at their respective ports A and B and prevents furher fluid flow to or from the counterbalance valve 68. he to the momentum attained by the heavy counterveig-hts 20 carried by the racks 15, and the effect of gravity should the tractor be positioned on a hillside, :xtreme pressures may be suddenly built up in the sysem resulting in damage or destruction of the components tfld conduits. The possibility of such pressure surges s eliminated in the present system by the relief valves '2. Irrespective of the direction of movement of the :ounterweights, the pressure within either conduit 66 or 57 will be limited by the relief valves 72 as these valves lirect the fluid to the opposite conduit and thereby automatically retard the counterweight movement by absorbng the energy. The continued movement of the counterleight racks and counterweights carried thereby after :entering of the control valve 60 will normally not be :reat and will not result in an undesirable lag in oper- .tion.

At any time the tractor should be operating on a lillside, the remote valves 69 of the counterbalance valve 58 will prevent loss of control of counterweight movenent, resulting from the effect of gravity. Assuming hat the tractor would be positioned transversely of the [inside and the counterweights would be on the low ide and that it is desired to extend the counterweights, t will be seen that gravity could exert such a force that :ontrol of movement may be lost. Merely venting the onduit 67 to the reservoir 64 could cause cavitation n the system resulting in dangerously rapid movement f the counterweights. Any tendency to cavitate would esult in loss of pressure in the conduit 66 and the renote valve 69 in the conduit 67 would close so as to etard or restrict the movement of the counterweights ln til the pressure has again built up in the conduit 66.

If it is desired to fully extend or retract the counterveights, the control valve 60 may be left in the opertting position thus permitting the hydraulic detent to unction and return the valve to center. When the pisons 39 reach the extreme ends of their stroke in each lirection, the pressure at the valve will increase due to :ontinued operation of the pump PF until the pressure caches the value at which the detent will operate.

The counterweight system of this invention surmounts hose problems encountered wherein the basic structure f tractor and side-boom frame are detrimental and retrictive to maximum retraction, to low center of gravty and to most eflicient design of rack and weights. this new method permits retraction of weights as far .s possible over the tractor tracks and permits the use )f block type design of counterweights. The weights and carrying racks are retracted to positions where they tre not subject to damage by contact with various obects such as trees, stumps, boulders, etc. and are at a high position above the crawlers out of the mud. Blocktype design of weights eliminates dead areas.

It is obvious that the further out the center of gravity of the mass of the counterweights is extended, the greater lift at the opposite side they can balance. Due to the magnitude of lift required by this type unit, great amounts of counterweight are required. Unfortunately, the quantity of counterweight required is usually detrimental to movement of tractor when not lifting. The further in the weight can be moved toward the longitudinal center line of the tractor, the beter the unit will steer, turn and move from place to place. Comparison of weight location on prior art units and the present unit indicates the advantage and necessity of swinging weights up and over the track crawlers as with the present unit.

This system of counterweighting eliminates complicated racks, linkage, safety links, etc. It includes one rack, one pivot point, one motivating cylinder or ram for each counterweight rack. The cylinder or ram doubles as a safety link. Pivot point and rack are within overall width and length of the tractor, eliminating necessity of removal of the weights and their racks. Also there is no obstruction below tractor tracks which would interfere with movement and steering.

This system of counterweighting enables use of simple, efficient cast counterweight blocks. Each block is held in place by permanent and adjustable locking devices. Construction of weights, minimum in number, enables quick removal and replacement. There are no dead corners when the weights are extended and they have maximum counterbalancing efliciency in that extended condition.

counterweight movement and synchronization are accomplished with this invention by special cylinders, plus checks and balances incorporated into a special hydraulic system. The requirements of such a hydraulic power train are complex and varied. The following requirements are met by this system:

(a) Synchronization of weights wherein the front and rear weights are extended and retracted approximately together.

(b) A throttling action when weights are stopped any place within the swing. Cushioning on maximum extension and retraction are accomplished by special cylinders, intermediate stopping is accomplished by cushioning valves. It is obvious that sudden starting and stopping of such a mass of weight could set up extreme shock loading throughout entire structure if this was not guarded against as provided for by this system.

(c) The characteristics of any dual hydraulic application motivation is for the oil to take the path of least resistance which, if the tractor is up or down hill, on side slopes, or externally affected wherein one or both weights are acted upon by gravity, the synchronization of said weights hydraulically is most difficult. Equalization of pressure and flow must be accomplished by special flow dividers and a system of hydraulic checks and balances. Obviously, the action and restriction of space does not lend itself to mechanical synchronization. These factors are effectively overcome with the system of this invention.

This invention obtains, without altering the basic carrying tractor, a most eflicient system of obtaining maximum counterweight extension within standard tractor widths, maximum retraction position Within standard tractor specifications, low profile, high clearance, safe, synchronized simple construction and maximum lift efliciency. Positioning, movement and synchronization are all accomplished in a totally dilferent manner from any known prior art unit.

According to the provisions of the patent statutes, the principles of this invention have been explained and have been illustrated and described in what is now considered to represent the best embodiment. However, it is to be understood that, within the scope of the appended claim,

the invention may be practiced otherwise than as specifically illustrated and described.

Having thus described this invention, what is claimed In combination with a tractor of the crawler type having first and second crawlers at its opposite sides, each with endless crawler tracks extending longitudinally in parallel relationship to the longitudinal center line of the tractor; a side attachment mounted on the first crawler at one side of the tractor so as to apply a load to the tractor having its center of gravity laterally outwardly of that crawler; counterbalance means at the opposite side of the tractor, said counterbalance means comprising a plurality of weight-carrying means having counterweights positioned thereon, and pivot means for mounting said weight-carrying means on the second crawler at the said opposite side of the tractor for swinging movement in a horizontal plane between a retracted position where they are in fore and aft relationship over the second crawler and within the outermost side extremity of the tracks of the second crawler so that the center of gravity of weights carried by said weight-carrying means will be over that crawler and an extended position laterally outwardly beyond said side extremity of the second crawler tracks so as to increase the distance from the center of gravity of the load to the center of gravity of the weights in order to provide for the weights to exert a maximum eifect in counterbalancing the load created by said attachment on the opposite first crawler of the tractor, said pivot means comprising pivot structures with vertically disposed pivot axes supported by the second crawler and spaced longitudinally thereof in a vertical plane disposed parallel to the center line of the tractor and parallel to and inwardly of the said outermost side extremity of the tracks of the second crawler, means for swinging said weight-carrying means between extended and retracted position, said weight-carrying means including horizontal support arms carried by said pivot structures and swingable in a horizontal plane above said second crawler at a right angle to said vertical plane and to which said swinging means is connected, all portions of said operating means and said support arms being within said outermost side extremity of said crawler tracks in retracted position of said weight-carrying means.

References Cited by the Examiner UNITED STATES PATENTS 2,493,602 1/1950 Sterrett 91-396 2,693,250 11/ 1954 Barrett 187-9 2,891,681 6/1959 Greivell 212-49 2,960,068 11/1960 Becker 91-396 X 3,033,219 5/1962 Erle 91-413 X 3,071,254 1/1963 Stilley 212-8 3,125,324 3/1964 Vivier 91-420 X 3,153,911 10/1964 Mark et a1 91-413 X EVON C. BLUNK, Primary Examiner SAMUEL F. COLEMAN, Examiner.

A. L, LEVINE, Assistant Examiner. 

